1. Field of the Invention
The present invention relates to polymers and nanoparticles. In particular, the present invention relates to polymer nanocomposites and methods producing the same.
2. Background of the Art
Nano-sized materials have been investigated for use in mechanically enhancing or stabilizing polyolefins materials. Semiconducting materials have been widely used for optical and electrical applications. Additionally, as the size reduces to several nanometers (quantum scale), semiconducting materials show size-dependent optical, electric and thermal properties different from the bulk semiconductor materials, known as quantum size effects, which make the semiconductor nanocrystals attractive for industrial applications and may give rise to new opportunities for functional polymer/semiconductor nanocomposites.
Incorporating semiconductor nanocrystals into polymeric matrices is a common way to fabricate optical and electrical devices, such as solar cells, light-emitting diodes (LED) and photovoltaic devices. However, without special surface functionalization, no current methods have been able to disperse semiconductor nanocrystals in polymers under nano-scale conditions and control the nanoparticles dispersion. Instead, large aggregates have been observed to form in polymers that limit the use of semiconductor nanocrystals in polymers for optical and electrical applications with desired mechanical and thermal properties and stability.
The semiconductor material zinc oxide (ZnO) is being investigated for use with polymers. ZnO is an important and attractive semiconducting material because of its distinguished properties in optics, photonics and electronics. For example, ZnO particles are used as an UV absorber in sunscreens and cosmetics. ZnO is also much more resistant to radiation damage than other semi-conductor materials. Moreover, ZnO is produced through wet-chemistry, which offers greater processing potential for use with polymers.
Many methods to incorporate semiconductor nanocrystals into polymers have had limited results. For example, ZnO particles were used as a mechanical reinforcement agent for polyolefins. However, to improve such properties as tensile modulus, the amount of ZnO particles used was of such an amount considered unacceptable for practical and economic purposes. ZnO particles blended with polyethylene to improve thermal stability have also been required in an amount considered unacceptable for practical and economic purposes. Alternative methods, such as preparing ZnO nanocomposites with organic modified ZnO to improve thermal stability were found to be too expensive and impractical for mass production. ZnO particles that have been investigated as a UV stabilizer for polyolefins were also observed to have detrimental effects on other properties of the materials including lost of transparency of composites.
Additionally, ZnO nanoparticles are observed to have inhomogeneous dispersion into polymer matrices by conventional processes, such as melt blending processes. Further, polymer matrices from conventional processes are observed to have large ZnO aggregates and both the size distribution ranging from 30-200 nm and the shapes of ZnO nanoparticles were not uniform. The presence of aggregates results in less than desired optical and/or electrical properties in the form of composites. Alternative processes including composition mixing of polymers and nanoparticles, in-situ polymerization of polymer/semiconductor nanocomposites, and in-situ synthesis of semiconductor/polymer nanocomposites are also observed to result in undesirable particle aggregates, inhomogeneous dispersion of the particles, and/or unacceptable levels of impurities, which all can lead to less than desirable composite physical and/or mechanical properties. Further, consistent nano-scaled dispersion of nanoparticles and controlling the state of dispersion have not yet been achieved.
To date, methods to incorporate ZnO particles and other materials into polymeric materials to form polymer nanocomposite materials for optoelectronic applications with improved stability or enhanced mechanical properties have met with limited success.
Accordingly, there is a need for forming polymer nanocomposites with effectively dispersed materials therein.